High-potential insulator.



EILIIHU THOMSON, 0F SWAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HIGHPOTENTIAL INSULATOB.

Specification of Letters Patent.

Patented Feb. 5, 1918.

To 'whom may concern:

it known that l, ELIHU THoMsoN, a

citizen of the United States, residing at Sivampscott, county of Essex, State of Massachusetts, have invented certain new1 anegl useful Improvements in High-Potential Insulators, oi which the following is a specilication. Mv invention relates to high potential .iiisulators which may be used for high potential terminals and the like and has for its general object an improvement in such devices.

When electric conductors carrying a high potential are brought ouh'from the casings used to contain. electricatf apparatus, such as transformers, switches and the like, or, when such conductors, which may form a sortion of transmission lines, are brought into buildings, it has been found that there is a very great tendency for the insulation surrounding the conductor to break down at or near the point where the conductor passes through the Wall of such casing or buildino.

The object ot my invention is to provide an insulator which will resist the tendenc to break flown when subjected to very higi differences of potential, and l accomplish this objiect by utilizing the principle of the noi'ieo1iclucting and insulating character of a very high vacuum, as a means for preventing such breakdown.

lf a vacuum vessel be sutliciently eX- hanstecl or if the vacuum within it be made substantially perfect, it becomes impossible to cause static discharge to pass through it upon the application of potentials of values with which We are familiar.

'It is well known that a vessel containing air 'will have through it a certain resistance to a static discharge, or the passage of an electric current. If such vessel be evacuated, as the vacuum is raised or the air pressure lowered, the resistance of thc air chamber in the vessel 'will decrease until it will reach a minimum. After this minimum is reached and as the vacuum is further increased or the vair pressure further diminished, the resistance of the chamber will increase, its resistance rising rapidly until it attains a high value. I employ this prineiple in the operation of my invention.

l am aware of the fait that it has been proposed 'to employ the increased resistance of a vacuum as a means for insulating conductors; but the'y constructions proposed, for this purpose have involved joints, gaskets, packings, and the like such as to render it impossible to Obtain a vacuum of such a high degree or an air pressure so loiv that the resistance of this vacuum is greater than would be the resistance of the air if no vacuum were used, or to maintain a high degree of vacuum for a substantially indefinite period, so that the. results could only be negative. As far as I am aware, therefore, insulators having vacua sulii ciently high to have insulating properties or reduced conductivity as compared -with the atmospheric ail` have not been used for practical purposes.

l accomplish the objectthen by surrounding the member or a plurality of members preferably formed of glass or quartz or some vitreous material having continuous Walls with vacuum chambers formed therein., Such chambers may then be evacuated in any -Well known manner and sealetl, and with this construction a high vacuum may be obtained, and, it the substances forming this insulating member be. properly chosen, such a vacuum may be maintained per mancntly.

For ay further uiulerstanding of my inot my invention conductor by a vention, reference may be had to tho ac-` companying drawing, in which Figure l shows in section a terminal emlioclying my invention, with a portion of the casing of an electrical apparatus to which such terminal may be connected; 3 shows a mocli lication of my invention, anni Figs. 3 and 4f show further modifications.

Referring lirst to Fig. l, l is a conductor which may have a. high voltage impressed upon it and be connected to a source of supply and to translating devices which have not been shown.

SurroundingY the conductor is an insulator Q having Walls 3 with .1 vacuum chamber -l formed therein. This insulating member, as shown, is jointless and may consist of a lengthened annulus or tubular member lengthened in. the direction of the conductor, and preferably made of glass or quartz or some other vitreous material of a kind which can be worked at a high temperature and which can be exhausted and sealed 21S perfectly as may be desired.

This annulus or tubular meinher may be lll() uns constructed by putting two tubes, one inside of the other, with a space between, and sealing' the ends together. Before completely closing or sealing-in the vacuum chamber, it is exhausted to perfect a vacuum possible and such a temperature that the occluded gases from the ualls are driven oft". This temperature will be almost that or usion. fitter such evacuation, the cl amber may be sealed in the usual manner. qWhile I have described a preferred construction for this insulating member, I do not limit myself to this construction, but any suitable construction for obtaining the desired result may be used.

Surrounding this insulating member Z is an insulating member 5, which may be formed oir porcelain or some other molded material and which mayv have formed upon it anges S for the purpose ot increasingl the leakage space over the exterior of the complete insulator in the Well understood manner.

ln conjunction with member I have shown insulating member 7, members and Z7 being; fastened to the casing 8 ofthe.`

transformer or the liire by means ont bolts 9.

is shown in the ligure, the casing oontains oil i0 and the bottom of the terminal is brought below the surface of the oil in the usual manner. It Will'be obvious, however, that 'While I have illustrated my inrention as applied a high potential terminal for transformers or switches and the like', is 'ch are placed in an oil-filled casing, i suitable modifications which will be readily understood by those skilled in the invention may be applied to insu loting the high Voltage conductors orming transmission lines and the like.

Immediately surrounding conductor l is shown insulating sleeve il, and the conductor is shown as rigidlj)Y fastened to the insulating members and i' by means of nuts l2.

Surrounding' member 2 is shovm a plastic material ifi, such as an insulating oil, resin or a mixture ei the saine, and the like.

It will be. obvious rrom an inspection of' 'the gure that in case a puncture or a breakdown ofthe insulation should take place, it .ias to naiss over the Whole length ,et the terminal or break through the insulating einher containing the vacuum chamber,

it is impossible for this to happen beca e high vacuum which exists in the ch practically a perfect insulator stand a very high voltage Without a current to low through it. As s explained above, it is necessariv that member shall be evacuated to such a l that the resistance across 'the lhamher is greater than that E' the chamber were i nreferably exhaust this chamber to such a high vacuum that an ionized gas discharge cannot take placeE across it, or a Vacuum higher than that olf-a Crookes tube. l

Referring non' to Fig. 2, I have shown a modification of my invention, consisting in surrounding the conductor l With a plurality of insulating members 2 having vacuum chambers 3 formed therein. These insulating members may be arranged as shown in a number ot rows, and preferably I so dispose the rows thatthe insulating members will break joints with each other, as may be seen from an inspection of the ligure.

Fig. 8 shows a further modification of my innention, the insulating members le with itaeuum chambers 32 being necked down so that one member will it or nest wit-,hin

the other in the mannerfshown, and therewill thus be a double vacuum layer at certain points.

In Fig. il, I have shown astill further modification of my invention consisting in vemploying a member l5, in which is formed space i4, through which the conductor may be run, and having a pluralityY of concentric vacuum chambers i6. Flanges 1T may, ir desired, be formed on the exterior of the insulating member for supporting the same in the usual manner.

Thilo these vacuum chambers may be made of an;T length, I prefer to make them as shown, with the ones nearest the conductor the longest, the length of the chambers decreasing as their distance from the conductor increases. By such a construe tiem-Where the voltage stress is the greatest between the conductor and the casing or wall through 'which it passes, the number oi' layers o1c insulating vacuum are the most numerous. This construction also has the advantage that if one vacuum layer is not quite so goed as another in insulation, that is, is not so Well exhausted or 'free from the remaining gases, the several vacuum cham-- bers malte up for each others deficiencies and the insulating value is the sum of' the having continuous, jointless Walls of vitreous material, capable of maintaining a vacuum for a .substantially indeimte period, the

chamber being evacuated to Such a degree that an ionization discharge cannot take place across the same.

Il l) menate? 2. An insulator comprising a vitreous annular member having walls with an integrally and hermetically. closed vacuum chamber formed therein, capable of maintaining a vacuum for a substantially indeiF nite period, the chamber being evacuated to such a degree that an ionization discharge cannot take place.

3. In combination, a conductor and an insulation for the same conmrising a plurality of integrally and hermctically closed vacuum chambers surrounding the same capable of maintaining a vacuum for a substantially indefiniter period, the chambers.

being evacuated to such a degree that an ionization discharge cannot take place across the saine.

4. A high potential terminal comprising a conductor, an insulating member Surrounding the same comprising a member having walls with an integrally and 11ermetically closed vacuum chamber' formed therein, the chamber being evacuated to such a degree that a cathode discharge cannot take place across the same, and a second insulating member surrounding said single member.

5. A high potential terminal comprising a conductor, an insulating member surrounding the same comprising a vitreous tubular member having walls with an integrally and hermetically closed vacuum chamber formed therein, capable of main taining a vacuum for a substantially indefinite period, the chamber being evacuated to such a degree that a cathode discharge cannot take place across the same, anda second insulating member surrounding said single member.

6. A high potential terminal comprising a conductor, an insulating member surrounding the same comprising` a vitreous tubular member having Walls with an integrally and hermeticallycloscdvacuumchamber formed thereimthe chamber being evacuated to such a degree that a cathode discharge cannot take place across the same, a second insulating membersurrounding Said single member. and means -for increasing the leakage surface of the second member.

7. A high potential insulating member comprising a plurality ot integrallyV and hermetically closed vacuum` chambers, ca` pable of maintaining a vacuum for a substantially indefinite period, the vacuum chambers being evacuated to such a degree that an ionization discharge cannot take place across the same. y

8. A high potential terminal comprising a conductor, an insulating member sur rounding the same comprising a member having walls with an integrally and hermctically closed vacuum chamber formed therein, capable of maintaining a high degree of vacuum ior a substantially indefinite period, the chamber being evacuated to' such a degree that an ionization discharge cannot take place across the same, a second insulating member surrounding said single member, and a plastic material between said members.

9.l A high potential terminal comprising a conductor, an insulating member surrcundingthe same comprising a vitreous tubular member having Walls with an integrally and hermetically closed vacuum chamber formed therein, capable of main* taining a high degree of vacuum for a substantially indefinite Period, the chamber being evacuated to such a degree that an ionization discharge cannot take place across the same, a second insulating member surrounding said single member, and a plastic material between said members.

In Witness whereof, I have hereunto set my hand this sixth day of January, 1913.

ELHU THOMSON. Witnesses:

JOHN A. McMANUs, Jr., FRANK G. HATTIE.

Sii 

